Hi everyone, we had a customer ask us to cut off a downtube mounting boss from a steel frame. He wants to run a dropper post with the cable routed through the downtube.

We highlighted we weren't entirely comfortable with the work, and agreed that if he's OK with that, we'll take on the work.

The work was done, and I'm now worried about frame integrity.

I'm worried the hole is too large. Looking for someone to help soundboard my concents. Is this hole too large, is the frame totaled, etc; any context would be appreciated.

Note the boss flang is still partially visible.




Best,
Dan

Just curious - downtube shifter mounts are normally welded/brazed to the tubing without a hole, or with a small hole where the 5mm screw goes. Did this bike have the braze-on mounted over this large hole, or did you grind through the tube while trying to grind off the braze-on?

My non-framebuilder opinion is that Surly tubing is likely thick enough to tolerate this hole, and that you could seal it and reinforce it with some judicious use of fiberglass and resin packed into the hole.


But I bow to the professionals:

Yea, you're correct - the bosses were brazed on, and there was a small hole behind the boss.

Preferably, we don't reinforce, but this is why we're here looking for discussion.

Did the hole have to be that big? I assume it will crack eventually, the hole quality doesn't look good to me. That's pretty important, holes should be smooth.

No it didn't need to be that big, I think the work just got a little away from me trying to smooth out the shape (oval to enable smooth cable entry, then teardrop to smooth out the edges). The frame eventually cracking is also my concern.

Interesting. How do the cables get around the BB shell?

If you're running a cable through the DT, then braze on some of these; https://framebuildersupply.com/colle...ver-2-10-packs
They'll strengthen the area.

As long as one keeps an eye on the holes for any developing cracks I would just ride the bike. Steel has that wonderful aspect of slow crack propagation and any cracks should be noticeable long before total separation.

Still just one more reason why I dislike internal routed cabling. Andy

I like that idea, though I think the frame will probably be fine without the brazed-on covers, because those frames use stout tubing.

Using one of those covers will require filing/sanding away all remnants of the original braze-on, so you just have the tube. The cover needs a near-perfect fit everywhere. Obviously all paint needs to be gone from the braze area. The cover doesn't need a high-temperature braze, it could be attached with soft silver solder and an air-propane torch, y'know the ones from the local hardware store that screw to the top of a little propane bottle. No oxygen needed other than ambient air.

The soft solder you want is tin-silver based, lead-free, and is stronger than lead-based solder. Though not as strong as brazing, we don't need the strength of brazing for this cap. It has a small amount of silver in it (typically 2%), unlike silver brazing filler (which is often erroneously called silver solder, though it is for brazing). You need the right flux, should be sold along with the solder. Example fram Ace Hardware, $12. Apply flux to the outside of the tube and the inside of the cap, where they touch. The solder flows and bonds at a very low temperature, so the main mistake beginners make is getting it too hot. Try it on a test piece of similar weight and thickness to see just how low a temperature it flows at. Heat the tube more than the braze-on. The cap will overheat quickly if you point the flame right at it. Only after the tube is getting close to soldering temperature should you let the flame point at the cap for a sec. Don't apply the solder to the work until the work is hot enough to suck the solder in by capillary action. The work should melt the solder, not the flame. Hold the part to keep it from moving while soldering. The tang of a file (or any such random piece of steel in your shop) can be laid on it to weigh it down, the other end of the file placed on some nearby surface so just the narrow tip is pushing down on the braze-on.

Buy the smallest amount of solder and flux that you can, unless you plan on doing some copper plumbing. Silver soft solder is useful for a few other things in the shop, but not too many. Soldering the ends of gear and brake cables comes to mind, if you're fancy. Me, I stopped soldering cable ends decades ago 'cuz I'm lazy, the crimp-on cable ends are good enough for me. But for a concours bike maybe. Soldered ends really are better than crimps, and when you get good at it it doesn't take long. But the parts have to be clean, free of oil/grease, and there's a risk of dripping flux on other things, like your toes if you wear sandals (don't do that!) or on the bike. I don't recall if the flux is corrosive if you leave drips on the bike, but you'll definitely not want it on rims or brake pads (if rim brake), or disk rotors, or tires.

Send us pics of the completed job if you do this.

I would be sorely tempted to pre-paint one of those cable covers and then epoxy it to the frame. It may or may not reinforce the hole, but it will cover it and look pro. No re-painting, no torches.



For soldering, if you aren't confident you can "tin" the back of the fitting with solder, then flux the frame and heat it in place to get that solder already on the part to stick. Won't work if you don't get the frame tube hot enough, though.

Oh hell yes!

I saw op's customer posted this on another site, and they are being advised not to ride it. I can't make a strong argument against that position. Can't post a link, but it's in r/bikewrench

Only advice I can give to OP is to avoid doing stuff like this in the future, there is no upside to it.

Do i see some residual thickness from the shift boss that remains around the hole? I have replaced tubes in the Surly frames and they are stout. Instead of simply cutting it up though, I would find a local frame builder and have them braze a plate around the hole as mentioned above.

I work in a bike shop as a wrench monkey and we would not have taken that job.
I'd consider it unsafe.
You now are libel for anything that happens to the rider, crash, etc., that can be attributed to the work done.
Good luck...

If they had a prior understanding that it wasn't recommended, the shop isn't liable. Especially if the owner has been advised by others not to ride it.

I'm just still curious how the cable is going to get into the seat tube.

Don't companies usually route the cable back out at the other end of the downtube and then back into the seat tube? I think I have seen that even with rather large aluminum or carbon tubes, and there is no room inside most steel frames

I wouldn't want to follow "legal" advice offered in this statement. I worked the ski retail service business a long time ago and we had a liability claim made against the shop because a father picked up the skis and boots we had done a release check and adjustment on. The equipment failed to pass the release check step, notes on the ticket were made and Dad signed off but either never told his kid or the kid didn't listen or think was important. Kid loses ski in mid air, suffers serious injuries, lawyer uncle comes after the shop for $. We spent a lot of time searching for that work ticket. We did find it and with the signed paper copy the case was dropped. Our lawyers told us that without that written and signed (by an adult...) we would have lost no mater what our nationally known release check technician would have said in court, he said she said and a hurt kid. You do the math. The shop suffered with lost man hours, a level of anxiety for months and even though we "won" the word got out to the school ski clubs and we lost at least one club contract for off season work on their loaner skis. Just because you might prevail doesn't mean that you spend a lot of $ and time if a lawsuit was to be sought.

My earlier post didn't address this aspect, legal liability and the cost of winning. I was only speaking to the frame's condition and what I would personally do about that. Andy

We've already found out the work wasn't done to the friend's expectations. If the friend is lax about checking for cracks and gets injured, they or their health insurance is going to go after the shop. Bad outcomes almost always end up in court, no matter if there was a friendship agreement in place. I'm pretty sure my LBS would consider themselves on the hook for a new frame in this case. I know they have replaced more than one frame when they messed one up getting a stuck seatpost out. Not really relevant in this thread, but they still take out stuck seatposts out even though it's a money loser overall. The local framebuilder that used to do it ruined a frame and stopped doing it.

I wasn't offering legal advice, just noting that the work was asked for, came out largely as expected (hole for cable housing) and the owner has no ability to claim that the bike was damaged and the shop has no legal ability to refuse giving the frame back.

Every time you repair a bike there may be a judgement call about whether a wheel will break a spoke, if those little marks on the steerer amount to carbon damage, if the rust on the chainstay is too deep, etc. So you tell the customer, make a recommendation and presume that it will largely be okay.

Most people on this thread seem to think that a Surly downtube is unlikely to fail from this hole and if it does fail it will come with a warning via cracks. So in the context of this particular instance, it seems like the shop is covered. Especially if the owner has written this down MTBR for all time.

That wont stop lawyers if there is a failure resulting in injury

IMHO shop should not have taken that on it seems skill/knowledge to do it right are lacking

best bet is to replace the frame with no mods ...... but i am conservative on these things, sturdy Surly tubing or not

I'd run cable down to into the BB shell, then guide it up into seattube with some other tools. If no joy, pull the cable out one side of BB shell with a hooked pick, then guide it up into the seattube. Then put housing on. Then choose a nice square taper cup-n-cone bottom bracket. I'd be tempted to cut another big 'ol hole in the frame, this one in the form of a BB shell inspection window to keep an eye on dropper cable/BB spindle interaction and wear.

The OP did what the customer wanted. The hole is slightly larger than it needed to be, but the request was to drill a hole in the downtube.
"Mr. Surly owner, did you not request that this bike mechanic - with no frame building background - drill a hole in your frame?"

Maybe Surly should be concerned since they don't have any warning stickers on the frame about hole drilling?

would you be willing to lose your business, etc. on that stand in a court of law?
i wouldn't...not a chance...not worth the risk but you go ahead...

Paging engineer Duragrouch ...

I'd guess that the frame is probably ok, since the down tube in that location is mostly focused in controlling the vertical plane, i.e., what happens when you hit a pothole or speedbump. And in the vertical plane, most of the work is being done by the top and bottom surfaces of the tube. It's much like an I-beam or W-section where most of the structural bending stiffness is coming from the top and bottom sections of the beam and the middle section (web) is really there to hold things together (and transfer sheer).

That said, there are torque forces at play from pulling on the bars and pushing a big gear. I'm not sure how the much that part of the downtube plays a roll in controlling those forces, but to be safe, I think those suggesting brazing on ports are making a good suggestion, for both strength and aesthetics. And since it's a Disk Trucker with stout 4130, epoxy might do the trick too.

But for sure, smooth out and round off any possible stress concentrators.

Then don't have any business fixing bikes, because the judgement calls happen all the time.